I think your mentioning of bytecodes comes from a misconception - a Delta carries source code, but it is *not* compiled when loaded into an image. The compilation is done in the "next step" - when you "apply" the Delta to the image (using SystemEditor to do it atomically).
Yes, I misunderstood what you meant by "compiler driven" and that you thought it was OK to use the compiler to apply the delta, but wanted to read the delta into the image without using a compiler.
Given that, I agree that JSON is a good match for your needs. I don't think you should use netstrings.
-Ralph